The present invention relates to electroacoustic novelties and, more particularly, to such novelties containing piezoelectric polymer film.
Traditional piezoelectric materials include certain naturally occurring crystals, such as quartz and Rochelle salts, as well as synthesized ceramics, such as barium titanate. These materials are capable of functioning as a speaker by converting electrical energy into sound or as a microphone by converting acoustic wave pressure into a corresponding electrical signal. In these electroacoustic applications, the piezoelectric material is typically mounted within a housing so that it can freely vibrate.
The above mentioned piezoelectric materials have been incorporated into a variety of articles to produce sound. For example, U.S. Pat. No. 4,597,099 issued Jun. 24, 1986 discloses the use of a piezoelectric crystal sound producer in a greeting card. A piezoelectric crystal, mounted in an appropriate housing, is electrically connected to an audio memory circuit. When the card is opened, a switching mechanism is activated and a musical tune is emitted from the vibrating piezoelectric material. This patent also discloses that the crystal sound producer may be incorporated into badges, emblems, pendants, lighters and keyholders.
Posters or display boards containing audio devices are known in the art. A conventional cone-type loudspeaker is mounted on the poster to deliver a voice or music message which coincides with the visual display image. The audio message is stored in a playback device, such as an audio memory circuit or a tape recorder. A mechanical switch mounted on the poster is used to activate the playback device to generate the audio message.
Piezoelectric polymer films, such as polyvinylidene fluoride, have also been used as transducer elements in both microphones and speakers. These materials are generally more flexible, lighter in weight and have a broader frequency response than the traditional piezoelectric materials. An example of the use of such films in a speaker application may be found in commonly assigned U.S. Pat. No. 4,638,207 issued Jan. 20, 1987. A piezoelectric polymer film is conformably adhered to either the inner or outer surfaces of an inflated member, such as a balloon. When the appropriate audio signal is supplied to the electrodes on the piezoelectric film and the balloon is filled with helium, the device functions as a floating speaker.